This invention relates to flat-panel displays of the cathode-ray tube (xe2x80x9cCRTxe2x80x9d) type, including the manufacture of flat-panel CRT displays. This invention also relates to the constitution and fabrication of structures that can be partially or fully utilized in flat-panel CRT displays.
A flat-panel CRT display basically consists of an electron-emitting component and a light-emitting component. The electron-emitting component, commonly referred to as a cathode, contains electron-emissive regions that emit electrons over a relatively wide area. The emitted electrons are suitably directed towards light-emissive elements distributed over a corresponding area in the light-emitting component. Upon being struck by the electrons, the light-emissive elements emit light that produces an image on the display""s viewing surface.
The electron-emitting and light-emitting components are connected together to form a sealed enclosure normally maintained at a pressure much less than 1 atm. The exterior-to-interior pressure differential across the display is typically in the vicinity of 1 atm. In a flat-panel CRT display of significant viewing area, e.g., at least 10 cm2, the electron-emitting and light-emitting components are normally incapable of resisting the exterior-to-interior pressure differential on their own. Accordingly, a spacer (or support) system is conventionally provided inside the sealed enclosure to prevent air pressure and other external forces from collapsing the display.
The spacer system typically consists of a group of laterally separated spacers positioned so as to not be directly visible on the viewing surface. The presence of the spacer system can adversely affect the flow of electrons through the display. For example, electrons coming from various sources occasionally strike the spacer system, causing it to become electrically charged. The electric potential field in the vicinity of the spacer system changes. The trajectories of electrons emitted by the electron-emitting device are thereby affected, often leading to degradation in the image produced on the viewing surface.
More particularly, electrons that strike a body, such as a spacer system in a flat-panel display, are conventionally referred to as primary electrons. When the body is struck by primary electrons of high energy, e.g., greater than 90 eV, the body normally emits secondary electrons of relatively low energy. More than one secondary electron is, on the average, typically emitted by the body in response to each high-energy primary electron striking the body. Although electrons are often supplied to the body from one or more other sources, the fact that the number of outgoing (secondary) electrons exceeds the number of incoming (primary) electrons commonly results in a net positive charge building up on the body.
It is desirable to reduce the amount of positive charge buildup on a spacer system in a flat-panel CRT display. Jin et al, U.S. Pat. No. 5,598,056, describes one technique for doing so. In Jin et al, each spacer in the display""s spacer system is a pillar consisting of multiple layers that extend laterally relative to the electron-emitting and light-emitting components. The layers in each spacer pillar alternate between an electrically insulating layer and an electrically conductive layer. The insulating layers are recessed with respect to the conductive layers so as to form grooves. When secondary electrons are emitted by the spacers in Jin et al, the grooves trap some of the secondary electrons and prevent them from escaping the spacers. Because fewer secondary electrons escape the spacers than what would occur if the grooves were absent, the amount of positive charge buildup on the spacers is reduced.
The technique employed in Jin et al to reduce positive charge buildup is creative. However, the spacers in Jin et al are relatively complex and pose significant concerns in dimensional tolerance and, therefore, in reliability. Manufacturing the spacers in Jin et al could be problemsome. It is desirable to have a relatively simple technique, including a simple spacer design, for reducing charge buildup on a spacer system of a flat-panel CRT display.
The present invention furnishes a variety of structures that are porous, at least along a face of each structure. Each of the porous structures, or a portion of each structure, is typically suitable for use in a spacer of a flat-panel CRT display. The present invention also furnishes techniques for manufacturing such porous-faced structures, including methods for manufacturing flat-panel displays.
A porous-faced spacer constituted according to the invention lies between a pair of plate structures of a flat-panel display. An image is supplied by one of the plate structures in response to electrons provided from the other plate structure. Somewhat similar to what occurs in Jin et al, the porosity along the face of the spacer creates facial roughness that prevents some secondary electrons emitted by the spacer from escaping the spacer. Accordingly, positive charge buildup on the spacer is reduced. The image is thereby improved.
In one structure configured according to the invention, multiple particle aggregates are bonded together in an open manner to form a solid porous body in which pores extend between the particle aggregates. The pores inhibit secondary electrons emitted by the porous body from escaping the body. Each particle aggregate contains multiple coated particles bonded together. Each of the coated particles is formed with a support particle and a particle coating that overlies at least part of the support particle.
The particle coatings preferably consist of material which, when struck by high-energy primary electrons, emit fewer secondary electrons than the material that forms the support particles. Candidate materials for the particle coatings are oxides and hydroxides of titanium, vanadium, chromium, manganese, iron, germanium, yttrium, zirconium, niobium, molybdenum, tin, cerium, praseodymium, neodymium, europium, and tungsten, including oxide and/or hydroxide of two or more of these metals. The particle coating material may also contain carbon.
Candidate materials for the support particles include a substantial number of oxides and hydroxides of metals, especially transition metals, and metal-like elements. In particular, the oxides and hydroxides of the non-carbon elements in Groups 3b, 4b, 5b, 6b, 7b, 8, 1b, 2b, 3a, and 4a of Periods 2-6 of the Periodic Table, including the lanthanides, are candidates for the support particles. This includes oxide and/or hydroxide of two or more of these non-carbon elements. As an example, when oxide and/or hydroxide of one or more of aluminum, silicon, titanium, chromium, iron, zirconium, cerium, and neodymium is utilized in the support particles, oxide and/or hydroxide of one or more of titanium, chromium, manganese, iron, zirconium, cerium, and neodymium is typically utilized in the particle coatings. The particle coatings are typically of different chemical composition than the support particles.
Various process sequences can be utilized in accordance with the invention to form a solid porous structure that contains multiple aggregates of coated particles. For instance, starting with (separate) aggregates of support particles, the support-particle aggregates can be bonded together in an open manner to form bonded aggregates of the support particles. Particle coatings are then provided over the support particles in the so-bonded aggregates to form the desired porous structure. Alternatively, the particle coatings can be provided over the support particles before or during the bonding of the support-particle aggregates. As another alternative, the particle coatings can be provided over (separate) support particles before or during particle bonding to form aggregates of the coated particles. The coated particle aggregates are then bonded together to form the desired solid porous structure.
When a porous-faced spacer of the present flat-panel display utilizes part or all of a porous structure containing multiple aggregates of particles bonded together in an open manner to form pores, the particles may include uncoated particles. That is, each of the particles need not have a particle coating that overlies a generally distinct, typically earlier formed, support particle.
In another structure configured according to the invention, a porous body has a face along which multiple primary pores extend into the body. A coating overlies a face of the porous body and extends along the primary pores so as to coat their surfaces without substantially closing them. The resulting pores in the combination of the porous body and the coating are referred to here as further pores. The coating normally consists principally of carbon. The carbon-containing coating typically has a thickness of 1-100 nm when the average diameter of the primary pores is 5-1,000 nm. Since the further pores are carbon-coated versions of the primary pores, the average diameter of the further pores is less than that of the primary pores and can be as little as 1 nm.
The thickness of the carbon-containing coating is normally highly uniform, especially along the pores. Specifically, the standard deviation in the thickness of the coating is preferably no more than 20%, more preferably no more than 10%, of the average thickness of the coating.
When the structure that contains the present carbon-containing coating is employed in a spacer of a flat-panel CRT display, the carbon in the coating normally emits fewer secondary electrons than what would occur from the underlying material of the porous body if the coating were absent. Making the coating thickness highly uniform enables the coating to be made quite thin without significantly exposing the underlying porous body and thereby increasing the secondary electron emission. The spacer normally dissipates less power as the coating is made thinner. Hence, achieving the present coating thickness uniformity leads, advantageously, to a reduction in power dissipation while avoiding an increase in secondary electron emission and an attendant increase in positive charge buildup on the spacer.
One technique for making a carbon-coated porous body according to the invention begins with precursor material that has multiple carbon-containing, normally organic, groups. A porous body is formed from the precursor material according to a process in which molecules of the precursor material cross-link while retaining at least part of the carbon-containing groups. When the precursor material is part of a liquidous composition, the ends of the carbon-containing groups typically move into the liquid so that the retained carbon-containing groups coat the surfaces of pores in the body.
The porous body is subsequently treated to remove non-carbon constituents of the retained carbon-containing groups, at least along exposed surface of the porous body. This may entail pyrolizing the retained carbon-containing groups or/and subjecting them to phenomena such as a plasma, an electron beam, ultraviolet light, or a reducing environment. In any event, the treating step furnishes the porous body with a rough face constituted principally with carbon.
Another technique for making a carbon-coated porous body in accordance with the invention begins with a porous body having a porosity of at least 10% along a rough face of the body. The porous body is subjected to carbon-containing chain molecules, each having at least one leaving species and at least one carbon-containing chain. The carbon-containing chain molecules chemically bond to the porous body, largely by reactions that involve only the leaving species. At least one leaving species is normally released from each carbon-containing chain molecule as it bonds to the porous body. Non-carbon constituents are subsequently removed from the so-bonded chain molecules. The porous body is thereby furnished with a carbon-containing coating.
In a further structure configured according to the invention, a solid porous film consists principally of oxide and/or hydroxide. Candidates for the oxide and/or hydroxide are oxides and/or hydroxides of non-carbon elements in Groups 3b, 4b, 5b, 6b, 7b, 8, 1b, 2b, 3a, and 4a of Periods 2-6 of the Periodic Table, again including the lanthanides. Preferably, the oxide and/or hydroxide includes oxide and/or hydroxide of one or more of silicon, titanium, vanadium, chromium, manganese, iron, germanium, yttrium, zirconium, niobium, molybdenum, tin, cerium, praseodymium, neodymium, europium, and tungsten, including oxide and/or hydroxide of two or more of these elements. The porous film has a porosity of at least 10% along a face of the film and an average thickness of no more than 20 xcexcm. The average electrical resistivity of the film is 108-1014 ohm-cm, preferably 109-1013 ohm-cm, at 25xc2x0 C.
A porous film that contains oxide and/or hydroxide is typically created by initially forming a liquid-containing film that includes precursor material of the oxide and/or hydroxide. The precursor material may be polymeric in nature and/or may consist of particles. The liquid-containing film is then processed to remove liquid from the film and convert it into a solid porous film having the porosity, thickness, and electrical resistivity properties specified above.
The film processing is normally conducted in such a way that atoms of the precursor material bond to one another in forming the solid porous film. Gas evolution from the precursor material and/or the liquid may be employed to create or enhance the solid film""s porosity. Also, the precursor material may include sacrificial carbon-containing, normally organic, material. After creating a solid film from the liquid-containing film, porosity is produced or enhanced in the solid film by removing non-carbon material, and typically also carbon, of the sacrificial part of the precursor material. A generally conformal coating may be provided over the solid porous film.
Each of the foregoing structures is, as mentioned above, utilized partially or wholly in a porous-faced spacer of a flat-panel display configured according to the invention. The porous-faced spacer lies between a first plate structure and an oppositely situated second plate structure. The first plate structure emits electrons. The second plate structure emits light upon receiving electrons emitted by the first plate structure.
Some high-energy primary electrons usually strike the spacer during display operation, causing the spacer to emit secondary electrons. The so-emitted secondary electrons are, on the average, normally of significantly lower energy than the primary electrons. Due to the porosity-produced roughness in the spacer""s face, the lower-energy secondary electrons are more prone to impact the spacer and be captured by it than what would occur if the spacer""s face were smooth. The lower-energy secondary electrons captured by the spacer cause relatively little further secondary electron emission from the spacer. The porosity along the spacer""s face thereby causes the overall amount of secondary electron emission to be reduced.
Primary electrons which strike the spacer include electrons that follow trajectories directly from the first plate structure to the spacer as well as electrons that reflect off the second plate structure after having traveled from the first plate structure to the second plate structure. The reflected electrons are generally referred to as xe2x80x9cbackscatteredxe2x80x9d electrons. While the flat-panel display can normally be controlled so that only a small fraction of the electrons emitted by the first plate structure directly strike the spacer, the backscattered electrons travel in a broad distribution of directions as they leave the second plate structure. As a result, electron backscattering off the second plate structure is difficult to control direction-wise. By inhibiting secondary electrons emitted by the present spacer from escaping the spacer, the spacer facial porosity also reduces spacer charging that would otherwise result from backscattered primary electrons striking the spacer.
In another aspect of the invention, a spacer situated between a pair of plate structures of a flat-panel display that operates in the preceding manner is provided with a directional resistivity characteristic for enhancing display performance. For this purpose, a substantially unitary primary layer overlies a face of a support body of the spacer. The spacer""s primary layer, although unitary in nature, is normally porous. The primary layer has a higher electrical resistivity parallel to the face of the support body than perpendicular to the support body""s face. More particularly, the average resistivity of the layer parallel to the body""s face is typically at least twice, preferably at least ten times, the average resistivity of the layer perpendicular to the body""s face.
By providing the spacer with the foregoing directional resistivity characteristic, the relatively low resistivity perpendicular to the face of the spacer""s support body enables charge that accumulates on the spacer due to primary electrons striking the spacer to be rapidly transferred from the outside of the spacer through the coating to the support body and then removed from the spacer. On the other hand, the relatively high resistivity parallel to the support body""s face serves to limit the current that flows through the primary layer from either plate structure to the other plate structure. Power dissipation is reduced. The display can operate efficiently without incurring significant charge buildup on the spacer. Also, the functions of controlling charge buildup and handling current flow from one plate structure to the other are substantially decoupled, thereby facilitating spacer design.
The primary layer of the spacer typically includes a base layer and a plurality of resistivity-modifying regions. The base layer overlies the face of the support body. The resistivity-modifying regions occupy laterally separated sites laterally surrounded by the base layer. The resistivity-modifying regions, preferably formed with carbon, are of lower average resistivity than the base layer. As a result, the resistivity of the primary layer is higher parallel to the support body""s face than perpendicular to the body""s face.
In accordance with the invention, a primary layer with a directional resistivity characteristic is typically created by initially forming a liquid-containing body that includes carbon particles and precursor material. The liquid-containing body is then processed to remove liquid from the body and convert it into a porous body through which most of the carbon particles largely penetrate. Atoms of the precursor material, which may be polymeric and/or consist of particles, normally bond to one another in forming the porous body. The porous body then constitutes a base layer of the primary layer, while the carbon particles constitute resistivity-modifying regions.
To the extent that the spacer used in the present flat-panel display has multiple levels of spacer material, the levels typically extend vertically relative to the electron-emitting and light-emitting components rather than laterally as in Jin et al. A spacer with vertically extending spacer-material levels is generally simpler in design, and can be fabricated to high tolerances more easily, than a spacer having laterally extending spacer-material levels. When the present spacer has multiple vertically extending levels of spacer material, reliability concerns associated with the spacer design are considerably less severe than those that arise with the spacer design of Jin et al. When the spacer used in the present display has only a single level of spacer material, the display essentially avoids the reliability concerns that arise in Jin et al. The net result is a large advance over the prior art.